Although many drugs are available that can control HIV replication and hinder progression towards AIDS, these drugs often have serious side-effects, and cannot cure the underlying infection. In contrast to other viral infections, the natural immune response to HIV-1 has proven incapable of eradicating the infection. We hypothesize that if ways could be found to overcome the factors that limit the effectiveness of the immune response towards HIV, this could greatly improve the control of infection with limited side-effects, and may even lead to a cure. This proposal is based on the discovery in our lab that the inability of most patient sera to neutralize typical primary HIV-1 isolates is not due to the lack of high titers of cross-reactive neutralizing antibodies or the absence in the patient's virus of potential neutralization targets recognized by those antibodies. Rather, we found that resistance to neutralization is due to the potent masking of those targets in the primary isolates. We have further demonstrated the presence of distinct mechanisms of masking that are mediated either by the V1V2 domain or by the V3 domain, and have identified specific sequences in both variable and conserved domains that modulate the extent of such masking. This understanding raises the possibility of the therapeutic utility of reagents that can unmask the potential targets to pre-existing neutralizing antibodies in patient sera. There is reason to believe that not only would such treatments lead to the potent inhibition of viral replication, but they would also allow the eradication of antigen-positive cells by normal antibody-mediated cytotoxic mechanisms. This latter effect represents an advantage of this approach over standard HAART reagents, which only target viral replication but have no effect against infected cells. The goals of this proposal are to develop efficient high-throughput screening assays that can be applied to existing small molecule libraries to identify such unmasking reagents, and in collaboration with the MLPCN to initiate such screening assays. PUBLIC HEALTH RELEVANCE: In most viral infections, the induced immune response is capable of controlling and eliminating the infection, but this is not true for HIV. This application is based on insights arising from our recent studies that show that most infected people do produce high titers of antibodies that identify conserved neutralization targets that are present in their replicating viruses, but inaccessible due to epitope masking. We are now proposing to develop and optimize a high throughput screening assay to identify compounds capable of interfering with the inter-subunit masking interactions in HIV-1 Env, thereby inducing conformational rearrangements that expose the conserved neutralization targets to neutralizing antibodies.